The fortified settlement of Borremose comprised a 140 x 90 m gravel bank surrounded by a moat with earth mounds on the inner side and connected to dry land by a 150 metres artificial cobbled road.The 450 m long moat, was 4 m wide, 1,5 m deep and with a flat bottom.
Borremose is known for and identified with a former fortified settlement dating from the Pre-Roman Iron Age (400-100 BC) (Martens 1994)(Martens 2004) (Martens 2007) (Martens 2010) .It was constructed during the 4th century BC, as one of the largest structures of its kind in Northern Europe, but was already abandoned during the 2nd century BC, when the houses were burned down and the whole site levelled to the ground.The northern part of the bog is heavily overgrown with trees and shrubs nowadays and is inaccessible in most places.Furthermore, due to industrial turf-production during and after World War II, large parts of the bog has turned into lakes.Because of this, such structures are sometimes referred to as "Borremose-fortifications", regardless of their whereabouts.
Borremose is a raised bog in central Himmerland, Denmark south east of the town of Aars.
The name translates directly as 'Borre'-bog, where 'Borre' might well be a derivation of the old word burgh meaning fortified place, as seen in many other place-names.
The settlement consisted of what seem to be ordinary long houses though without byre.
At the most about 20 long houses may have been in use at the same time.
After the excavation, the house sites were marked with turf walls so the settlement plan is visible for the visitor today; furthermore, the moats have been emptied and the walls reconstructed.
For a long time, the Borremose-fortification was the only known Iron Age fortified settlement in Scandinavia, until a similar construction was discovered at Lyngsmose near Ringkøbing in western Jutland in 1999.